Various agents used in the practice of anesthesia were applied in fifty five healthy postmenopausal female volunteers in order to investigate their hypothalamo hypophyseal response to these drugs, by measuring PRL and TSH levels in peripheral blood. Selection of volunteers, separation of blood specimens and RIA techniques were performed according to international standards. Our results show that thiopental, ketamine and dehydrobenzperidine increase PRL levels significantly (p less than 0.05-0.0025) while fentanyl and diazepam do not alter basal PRL values (p greater than 0.10). It is assumed that thiopental and ketamine may affect the hypothalamo hypophyseal axis through a cholinergic mechanism, whereas dehydrobenzperidine through a dopaminergic one. Atropine reduces the increase in PRL levels caused by thiopental and ketamine, while it does not affect PRL high levels induced by dehydrobenzperidine. TSH levels remain unaffected by all drugs, though ketamine shows a statistically indicative mild tendency to increase PRL levels (p less than 0.10). The fact that TSH values remain the same may be due either to the slower release of TSH stores, or to the involvement of a somatostatin-related mechanism in addition to the one described herein.